Nitrogen dynamics and microbial food web structure during a summer cyanobacterial bloom in a subtropical,shallow, well-mixed,eutrophic lake (Lake Taihu,China)

Nitrogen dynamics and microbial food web structure were characterized in subtropical, eutrophic, large (2,338 km²), shallow (1.9 m mean depth), and polymictic Lake Taihu (China) in Sept–Oct 2002 during a cyanobacterial bloom. Population growth and industrialization are factors in trophic status deterioration in Lake Taihu. Sites for investigation were selected along a transect from the Liangxihe River discharge into Meiliang Bay to the main lake. Water column nitrogen and microbial food web measurements were combined with sediment–water interface incubations to characterize and identify important processes related to system nitrogen dynamics. Results indicate a gradient from strong phosphorus limitation at the river discharge to nitrogen limitation or co-limitation in the main lake. Denitrification in Meiliang Bay may drive main lake nitrogen limitation by removing excess nitrogen before physical transport to the main lake. Five times higher nutrient mineralization rates in the water column versus sediments indicate that sediment nutrient transformations were not as important as water column processes for fueling primary production. However, sediments provide a site for denitrification, which, along with nitrogen fixation and other processes, can determine available nutrient ratios. Dissimilatory nitrate reduction to ammonium (DNRA) was important, relative to denitrification, only at the river discharge site, and nitrogen fixation was observed only in the main lake. Reflecting nitrogen cycling patterns, microbial food web structure shifted from autotrophic (phytoplankton dominated) at the river discharge to heterotrophic (bacteria dominated) in and near the main lake.     

太湖夏季浮游细菌群落多样性的空间格局

为了研究太湖夏季浮游细菌群落多样性与水体营养盐的关系,在太湖全湖范围内开展了一次大规模浮游细菌采样调查,分析了太湖不同湖区浮游细菌丰度和多样性组成。研究发现,浮游细菌丰度在不同湖区中存在明显的空间差异,从北部和西部湖区沿湖流向东南方向至湖心和南部沿岸再到东部湖区呈下降趋势,这与太湖水体营养水平从高到低变化趋势一致。浮游细菌丰度与营养盐浓度回归分析结果显示,总磷（TP）与细菌丰度存在较好的正相关（R2=0.6392,n=29,P0.01）,而总氮（TN）与细菌丰度无显著相关（R2=0.0663,n=29,P0.05）。因此,磷是太湖夏季浮游细菌生长的限制因子。不同湖区营养盐与浮游细菌群落多样性也具有显著的正相关,随着营养水平的升高,浮游细菌多样性增加。此外,细菌群落的组成在不同湖区间亦具有明显的空间异质性,与不同湖区营养水平空间变化一致。研究结果将有助于人们更好地理解淡水湖泊中微生物循环和生态系统功能。       

Anaerobic methane oxidation potential and bacteria in freshwater lakes: Seasonal changes and the influence of trophic status

Nitrite-dependent anaerobic methane oxidation (n-damo), mainly carried out by n-damo bacteria, is an important pathway for mitigating methane emission from freshwater lakes. Although n-damo bacteria have been detected in a variety of freshwater lakes, their potential and distribution, and associated environmental factors, remain unclear. Therefore, the current study investigated the potential and distribution of anaerobic methanotrophs in sediments from Erhai Lake and Dianchi Lake, two adjacent freshwater lakes in the Yunnan Plateau with different trophic status. Both lakes showed active anaerobic methane oxidation potential and harbored a high density of n-damo bacteria. Based on the n-damo pmoA gene, sediment n-damo bacterial communities mainly consisted of Candidatus Methylomirabils oxyfera and Candidatus Methylomirabils sinica, as well as novel n-damo organisms. Sediment anaerobic methane oxidation potential and the n-damo bacterial community showed notable differences among seasons and between lakes. The environmental variables associated with lake trophic status (e.g. total nitrogen, ammonia nitrogen, nitrate nitrogen, and total organic carbon) might have significant impacts on the anaerobic methane oxidation potential, as well as the abundance and community structure of n-damo bacteria. Therefore, trophic status could determine the n-damo process in freshwater lake sediment.     

Abundance and community composition of ammonia-oxidizing archaea and bacteria in two different zones of Lake Taihu

The abundance and community composition of ammonia-oxidizing archaea and ammonia-oxidizing bacteria in the surface sediments of 2 different zones (Meiliang Bay and Eastern Lake Taihu) of Lake Taihu were investigated using real-time quantitative polymerase chain reaction and clone libraries. The amoA gene copy numbers in the surface sediment of Meiliang Bay ranged from 4.91?× 10(5) to 8.65?× 10(6) copies/g dry sediment for the archaeal amoA gene and from 3.74?× 10(4) to 3.86?× 10(5) copies/g dry sediment for the bacterial amoA gene, which were significantly higher than those of Eastern Lake Taihu (P?< 0.05). Concentrations of ammonia (NH(4)(+)), total nitrogen, organic matter, and pH of the sediments exhibited significantly negative correlations with the abundance of ammonia-oxidizing archaea or ammonia-oxidizing bacteria (P?< 0.05 or P?< 0.01, respectively). The potential nitrification rates show remarkable correlations with the copy numbers of the archaeal amoA gene. Diversity of the archaeal amoA gene in Eastern Lake Taihu was significantly higher than that of Meiliang Bay, whereas the bacterial amoA gene diversity was comparable for the 2 lake zones. The data obtained in this study would be useful to elucidate the role of ammonia-oxidizing archaea and ammonia-oxidizing bacteria in the nitrogen cycle of freshwater ecosystems.     

冬季太湖表层底泥产毒蓝藻群落结构和种群丰度

应用荧光定量PCR对冬季太湖不同湖区底泥表面有毒微囊藻和总微囊藻种群丰度进行调查,同时基于PCR-DGGE技术对底泥中有毒微囊藻群落结构进行分析。结果表明:微囊藻在太湖底泥表面分布广泛,所有采样点都检测到有毒微囊藻存在,且不同湖区有毒微囊藻和总微囊藻种群丰度存在显著差异,有毒微囊藻和微囊藻基因型丰度范围分别为1.23×10⁴-3.75×10⁶拷贝数/g干重和2.56×10⁴-1.07×10⁷ 拷贝数/g干重,有毒微囊藻与微囊种群丰度的比例为4.8％-35.2％;DGGE指纹图谱显示,冬季太湖不同湖区表层底泥中有毒微囊藻群落结构相似性较高,相似性系数为70.2％-96.0％。虽然不同湖区基因型组成存在差异,但所有样品中占优势的基因型是一致的。同时发现,优势基因型所占的比例与样品的香农多样性指数呈负相关。序列分析表明,mcyA序列长度为291bp,序列相似性超过97％。综合定量PCR结果和底泥中叶绿素a和藻蓝素浓度的测定结果,可以得出2010年冬季太湖蓝藻越冬主要集中在梅梁湾、竺山湾、贡湖湾和湖心。通过建立荧光定量PCR分析方法,为研究湖泊底泥中蓝藻种群丰度动态变化奠定了基础。     

Effects of resuspension and eutrophication level on summer phytoplankton dynamics in two hypertrophic areas of Lake Taihu,China

The composition of summer phytoplankton communities in two highly eutrophic areas of Lake Taihu, a large, shallow water body in China (area 2,338 km²; mean depth 2.0 m), was studied in relation to selected environmental variables. Both areas have multiple uses, including drinking water supply, fisheries, and recreation. The first area, Meiliang Bay, is much closer to central lake and subjected to wind-driven sediment resuspension, while the second, at Wuli Lake, is less affected by wave action but is considered more nutrient-rich due to its proximity to human inhabitation. By comparing two lake areas, we attempt to advance the understanding and management of different regions of shallow lakes, mainly differing in resuspension levels and eutrophication levels. A comparison of these two lake areas indicated a higher standing crop of phytoplankton in Wuli Lake than in Meiliang Bay. Canonic Correspondence Analysis indicated that nutrient status and sediment resuspension were the principal factors influencing phytoplankton composition in both areas. The dominant algal group in Meiliang Bay comprised immobile R-type strategists (Reynolds in Growth and reproductive strategies of freshwater phytoplankton, 1988), including filamentous diatoms and green algae (Aulacoseira granulate and Planctonema lauterbornii), and recruitment-beneficial RS-type strategists, mainly the colonial cyanobacteria (Microcystis spp.). The community of Wuli Lake was dominated by S-strategists, principally motile flagellates (Cryptomonas spp.) and C-strategists including small nonmotile centric diatoms and chlorococcal green algae.     

基于PCA和SOM模型的龙感湖水质时空动态研究

为评估湖泊渔业模式转型阶段水环境的时空动态,选择长江中下游典型湖泊龙感湖为研究地点,于2017—2018年对该湖的黄梅水域和宿松水域进行周年季度水质监测,通过主成分分析(PCA)和自组织特征映射人工神经网络(SOM)模型定量分析了水体理化参数的时空变化特征,采用综合营养状态指数法(TLI)对水体富营养化状况进行了评价。PCA分析结果表明,龙感湖宿松水域和黄梅水域的水质差异较小,季节动态明显。全湖氨氮夏季平均浓度高达0.64 mg/L;总氮夏季平均浓度为2.30 mg/L,冬季平均浓度为1.04 mg/L;叶绿素a夏季平均含量达95.28μg/L,秋季平均浓度为28.30μg/L; pH夏季最高,达9.27;总磷冬季最高,平均为0.22 mg/L; TLI指数表明龙感湖除秋季属于轻度富营养水体外,其他3个季节均属于中度富营养状态。SOM模型结果具有可视化强的优点,能够更清晰和直观地反映龙感湖水质的时空分布动态。围栏拆除和禁渔等管理措施有助于湖泊渔业环境修复和资源恢复,建议对渔业模式转型后的湖泊生态系统变化进行长期跟踪监测评估。     

The bacterioplankton of Lake Taihu,China: abundance,biomass, and production

Abundance, biomass and production of pelagic bacteria were examined over one year at monthly sampling intervals across a trophic profile in Meiliang Bay, Lake Taihu. With the lowest density in the open lake, the bacterial abundance showed a clear trend in relation to trophic status. The carbon content per cell was higher in autumn and winter, and the opposite was true for bacterial biomass. Bacterial ³[H]-TdR and ¹⁴[C]-Leu incorporation rates, cell production, turnover times and carbon production varied during the annual cycle at different sites. The ratio of bacterial production to primary production was high, independently of the method used, indicates that the microbial food web in Lake Taihu is an important component of the total food web of the lake and dominated by external inputs. Electronic supplementary material Supplementary material is available for this article at and is accessible for authorized users     

Environmental changes in Lake Taihu during the past century as recorded in sediment cores

The Lake Taihu drainage basin is an economically developed area with some of the highest population densities in China. The lake has deteriorated due to ecological destruction and eutrophication. Three short sediment cores from eastern, northeastern and southwestern Lake Taihu were collected. Total organic carbon (TOC), total nitrogen (TN), pigments, elements and particle size were analyzed for the purpose of understanding past trophic status and pollution levels. Sedimentation rates were based on ¹³⁷Cs or ²¹⁰Pb methods. Results indicated that sediment particle size became coarser since the 1920s, and the lake was contaminated by heavy metals, such as Cu and Zn, since the 1970s. A remarkable increase in eutrophication since the 1980s due to increased loading of untreated effluents from industry, agriculture and urbanization is reflected by total organic carbon, total nitrogen and pigments in the studied cores. However the onset times of eutrophication in different parts of Lake Taihu were not synchronous.     

Dominant genera of cyanobacteria in Lake Taihu and their relationships with environmental factors

Cyanobacterial blooms in freshwaters have become one of the most widespread of environmental problems and threaten water resources worldwide. Previous studies on cyanobacteria in Lake Taihu often collected samples from one site (like Meiliang Bay or Zhushan Bay) and focused on the variation in patterns or abundance of Microcystis during the blooming season. However, the distribution of cyanobacteria in Lake Taihu shows differing pattern in various seasons. In this study, water samples were collected monthly for one year at five sites in Lake Taihu with different trophic status and a physicochemical analysis and denaturing gradient gel electrophoresis (DGGE) were conducted. DGGE fingerprint analysis showed that Microcystis (7/35 bands) and Synechococcus (12/35 bands) were the two most dominant genera present during the study period at all five sites. Cyanobium (3/35 bands) was the third most common genus which has seldom been previously reported in Lake Taihu. Redundancy analysis (RDA) indicated that the cyanobacterial community structure was significantly correlated with NO₃^--N, COD_Mn, and NH₄⁺-N in the winter and spring, whereas it was correlated with water temperature in the summer and autumn. Limiting the nutrient input (especially of N and C loading) in Lake Taihu would be a key factor in controlling the growth of different genera of cyanobacteria.     

Current status and future tendency of lake eutrophication in China

Current trophic status and trend of Chinese freshwater lakes were investigated in this study. The results showed that all lakes studied were commonly undergoing the eutrophica-tion process, water quality decreased and lake's ecosystem is being declined. Most of the urban lakes are facing serious eutrophication. Many medium-sized lakes are in metrophic or eutrophic status, some local water are even approaching the hypertrophic level. The famous five freshwater lakes in China have entered into eutrophication in the condition of higher nutrient load. Lake Taihu, Hongze and Caohu are already in eutrophic state. Eutrophic lakes are mainly distributed in the middle and lower reaches of Yangtze River and Yungui plateau. Lake eutrophication developed rapidly. Among the 34 lakes studied in 1970's, most of lakes were in the mesotrophic status, mesotrophic water area accounted for 91.8%. With the nine year of 1978-1987 the area percentage of oligotrophic lakes decreased from 3.2% to 0.53%, and that of eutrophic lakes increased from 5.0% to 55.01%. Recent data showed 57.5% lakes were in eutrophic and hyper trophic status of the 40 surveyed lakes. Eutrophic trend of Lake Taihu, Chaohu and Xuanwu in the region of the middle and lower reaches of Yangtze River was predicated using the ecological stress model. The results showed that in 2008 Lake Taihu, Chaohu and Xuanwu might be of eutrophication, eutrophication and hypertrophication, respectively if no control measurement is taken. Provided the pollution water treatment rate is 60% in 2030, approximately 30 billion ton pollution water would still be discharged directly in the lakes. Therefore, in 2030 the urban lakes in China might be eutrophication or hypertrophication, and most of the medium-sized lakes at the urban-rural fringe might be in eutrophication or hypertrophication. The famous five biggest freshwater lakes in China might be eutrophication if control countermeasures are taken as now. Lake eutrophication has become a serious environmental problem in China. Based on the domestic and foreign experiences of the eutrophic control technologies, both nutrient pollution control and lake ecological restoration should be carried out and this may be the guidance for the eutrophic control of lakes in China.     

Phytoplankton Cell Lysis after Water Bloom in a Eutrophic Freshwater Lake Taihu (China)

The phytoplankton lysis rates in the different eutrophic regions of Lake Taihu were determined based on the activities of particle and dissolved esterase, as well as the decay rate of the latter, from August 2009 to March 2010. Two peaks were observed for the chlorophyll a concentration, one in September 2009 and another in January 2010. The highest phytoplankton lysis rates observed in October were associated with the decay of the summer bloom, whereas the minimum lysis rates observed in January were associated with the winter bloom. The highest cell lysis rates in Meiliang Bay, Lake centre, and Gonghu Bay were 0.67, 0.77, and 0.68 d^–1, respectively, whereas the lowest lysis rates in these regions were 0.03, 0.01, and 0.05 d^–1, respectively. Water temperature showed an apparent indirect effect on lysis rate. In addition, a significant inverse relationship was observed between lysis rates and nitrate concentration in the three lake regions, which suggests that phytoplankton cell lysis is associated with changes in nitrate concentration. (© 2011 WILEY‐VCH Verlag GmbH & Co. KGaA, Weinheim)     

太湖竺山湾沉积物中氨氧化原核生物的垂直分布与多样性

原核生物驱动的氨氧化过程对于富营养化湖泊的氮循环具有重要意义。为了解太湖藻型湖区沉积物中氨氧化原核生物的垂直分布和多样性特征,采用分子生态学方法,对竺山湾沉积物剖面中氨单加氧酶基因(amoA)或16S rRNA基因等特征分子标记的变化和序列特征进行了分析。结果表明,氨氧化细菌(ammonia-oxidizing bacteria,AOB)和氨氧化古菌(ammonia-oxidizing archaea,AOA)共存于沉积物各层。AOB的优势种在5cm深度以下发生明显改变,这可能与沉积物氧化还原电位及铵态氮的变化有关;所有细菌amoA序列均属亚硝化单胞菌(Nitrosomonas)。AOA群落结构自表层至7cm深度变化不大,所有古菌amoA序列分属泉古菌CG1.1b和CG1.1a两大类群,这可能与太湖形成历史上的海陆交替过程有关。此外,沉积物各层均未发现典型厌氧氨氧化(anaerobic ammonium oxidation,anammox)细菌16S rRNA基因序列。这些发现丰富了对太湖藻型湖区氨氧化原核生物分布、多样性及环境调控原理的认识,对理解富营养化湖泊氨氧化规律、认识湖泊生态系统氮循环功能具有借鉴意义。     

The photosynthetic and growth rate responses of two freshwater angiosperms in lakes of different trophic status: responses to light and dissolved inorganic carbon

SUMMARY 1. Two rooted freshwater macrophytes ( Lagarosiphon major (Ridley) Moss; Myriophyllum triphyllum Orchard) were grown in two lakes of differing trophic status on sediments collected from an eutrophic lake. In the two experiments (summer and winter) in the oligotrophic lake (Lake Taupo, New Zealand), the relative growth rates of both species were approximately double those recorded in the experiments in the eutrophic take (Lake Rotorua, New Zealand). These growth responses occurred even though the light and temperature regimes were similar at the experimental sites in both lakes and the concentrations of inorganic nutrients were higher in the eutrophic lake water.
2. Dissolved inorganic carbon (DIC) analysis of both lake waters indicated that the oligotrophic water had approximately 10-fold more DIC than the eutrophic water. This corresponded, at natural pH, to a 2-fold higher concentration of free-CO₂ in the oligotrophic lake water (49 μM) than in the eutrophic lake water (23 μM). Photosynthetic experiments demonstrated that the maximum rates of photosynthesis were 2.46 and 2.25-fold higher in L. major and M. triphyllum , respectively, when the shoots were incubated in Lake Taupo water at Lake Taupo levels of free-CO₂ relative to Lake Rotorua water at Lake Rotorua levels of free-CO₂.
3. It is concluded that these differences in photosynthetic rates would lead approximately to a 2-fold difference in growth rate, thus explaining the growth responses observed in the field experiments.     

Sediment microbial community structure and mercury methylation in mercury-polluted Clear Lake, California

Spatial and temporal variations in sediment microbial community structure in a eutrophic lake polluted with inorganic mercury were identified using polar lipid fatty acid (PLFA) analysis. Microbial community structure was strongly related to mercury methylation potential, sediment organic carbon content, and lake location. Pore water sulfate, total mercury concentrations, and organic matter C/N ratios showed no relationships with microbial community structure. Seasonal changes and changes potentially attributable to temperature regulation of bacterial membranes were detectable but were less important influences on sediment PLFA composition than were differences due to lake sampling location. Analysis of biomarker PLFAs characteristic of Desulfobacter and Desulfovibrio groups of sulfate-reducing bacteria suggests that Desulfobacter-like organisms are important mercury methylators in the sediments, especially in the Lower Arm of Clear Lake.     

Bacterial Diversity and Geochemical Profiles in Sediments from Eutrophic Azorean Lakes

In the Azores, the advanced trophic state of the lakes requires a fast intervention to achieve the good ecological status prescribed by the Water Framework Directive. Despite the considerable effort made to describe the phytoplankton growing on the water column, the lack of information regarding the microbial processes in sediments is still high. Thus, for the successful implementation of internal management actions, the present work explored the relationships between geochemical profiles and dominant members of the bacterial community in sediments from eutrophic Azorean lakes. Lake Azul geochemical profiles were quite homogeneous for all parameters, while in lake Furnas the total iron profile presented a peak below the aerobic layer. For lake Verde, the concentrations of all studied parameters (20 ± 2% loss-on-ignition; 2.10 ± 0.08 mg g^?1 total phosphorus; 1.31 ± 0.50 mg g^?1 total nitrogen; 8.06 ± 0.13 mg g^?1 total iron) in the uppermost sediment layer were approximately two times higher than the ones in sediments from other lakes, decreasing with sediment depth. The higher amounts of phosphorus and organic matter in lake Verde suggested a higher internal contribution of phosphorus to eutrophication. The dominant members of the sediment bacterial community, investigated by denaturing gradient gel electrophoresis, were mostly affiliated to Proteobacteria phylum (Alpha-, Delta-, and Gamma-subclasses), group Bacteroidetes/Chlorobi and phylum Chloroflexi. The Cyanobacteria phylum was solely detected in sediments from lake Verde and lake Furnas that presented the highest amounts of nitrogen and phosphorus both in the water column and sediments, while the other phyla were detected in sediments from the three studied lakes. In conclusion, management measurers to achieve the good ecological status until 2015 should be distinct for the different lakes taking into account the relative magnitude of the nutrient sources and the bacterial diversity in sediments.     

Current status and future tendency of lake eutrophication in China

Current trophic status and trend of Chinese freshwater lakes were investigated in this study. The results showed that all lakes studied were commonly undergoing the eutrophication process, water quality decreased and lake’s ecosystem is being declined. Most of the urban lakes are facing serious eutrophication. Many medium-sized lakes are in metrophic or eutrophic status, some local water are even approaching the hypertrophic level. The famous five freshwater lakes in China have entered into eutrophication in the condition of higher nutrient load. Lake Taihu, Hongze and Caohu are already in eutrophic state. Eutrophic lakes are mainly distributed in the middle and lower reaches of Yangtze River and Yungui plateau. Lake eutrophication developed rapidly. Among the 34 lakes studied in 1970’s, most of lakes were in the mesotrophic status, mesotrophic water area accounted for 91.8%. With the nine year of 1978–1987 the area percentage of oligotrophic lakes decreased from 3.2% to 0.53%, and that of eutrophic lakes increased from 5.0% to 55.01%. Recent data showed 57.5% lakes were in eutrophic and hypertrophic status of the 40 surveyed lakes.

Eutrophic trend of Lake Taihu, Chaohu and Xuanwu in the region of the middle and lower reaches of Yangtze River was predicated using the ecological stress model. The results showed that in 2008 Lake Taihu, Chaohu and Xuanwu might be of eutrophication, eutrophication and hypertrophication, respectively if no control measurement is taken. Provided the pollution water treatment rate is 60% in 2030, approximately 30 billion ton pollution water would still be discharged directly in the lakes. Therefore, in 2030 the urban lakes in China might be eutrophication or hypertrophication, and most of the medium-sized lakes at the urban-rural fringe might be in eutrophication or hypertrophication. The famous five biggest freshwater lakes in China might be eutrophication if control countermeasures are taken as now.

Lake eutrophication has become a serious environmental problem in China. Based on the domestic and foreign experiences of the eutrophic control technologies, both nutrient pollution control and lake ecological restoration should be carried out and this may be the guidance for the eutrophic control of lakes in China.

     

Current status and future tendency of lake eutrophication in China

Current trophic status and trend of Chinese freshwater lakes were investigated in this study. The results showed that all lakes studied were commonly undergoing the eutrophication process, water quality decreased and lake's ecosystem is being declined. Most of the urban lakes are facing serious eutrophication. Many medium-sized lakes are in metrophic or eutrophic status, some local water are even approaching the hypertrophic level. The famous five freshwater lakes in China have entered into eutrophication in the condition of higher nutrient load. Lake Taihu, Hongze and Caohu are already in eutrophic state. Eutrophic lakes are mainly distributed in the middle and lower reaches of Yangtze River and Yungui plateau. Lake eutrophication developed rapidly. Among the 34 lakes studied in 1970's, most of lakes were in the mesotrophic status,mesotrophic water area accounted for 91.8%. With the nine year of 1978-1987 the area percentage of oligotrophic lakes decreased from 3.2% to 0.53%, and that of eutrophic lakes increased from 5.0% to 55.01%. Recent data showed 57.5% lakes were in eutrophic and hypertrophic status of the 40 surveyed lakes.Eutrophic trend of Lake Taihu, Chaohu and Xuanwu in the region of the middle and lower reaches of Yangtze River was predicated using the ecological stress model. The results showed that in 2008 Lake Taihu, Chaohu and Xuanwu might be of eutrophication, eutrophication and hypertrophication, respectively if no control measurement is taken. Provided the pollution water treatment rate is 60% in 2030, approximately 30 billion ton pollution water would still be discharged directly in the lakes. Therefore, in 2030 the urban lakes in China might be eutrophication or hypertrophication, and most of the medium-sized lakes at the urban-rural fringe might be in eutrophication or hypertrophication. The famous five biggest freshwater lakes in China might be eutrophication if control countermeasures are taken as now.Lake eutrophication has become a serious environmental problem in China. Based on the domestic and foreign experiences of the eutrophic control technologies, both nutrient pollution control and lake ecological restoration should be carried out and this may be the guidance for the eutrophic control of lakes in China.     

Sediment phosphorus cycling in a large shallow lake: spatio-temporal variation in phosphorus pools and release

Sediment and water column phosphorus fractions were recorded monthly for one year (April 2004–April 2005) in a shallow lake recovering from nutrient pollution (Loch Leven, Scotland). Equilibrium phosphate concentration (EPC0) and gross sediment phosphorus (P) release rates were estimated from laboratory experiments. Pore water and organic P pools were lowest during warm water periods whereas bottom water P was lowest during cold water periods. Reductant-soluble, organic, metal oxide-adsorbed, residual and sediment total phosphorus pools all varied significantly with overlying water depth. Short-term, high magnitude, redox initiated P release events occurred in late summer and winter as a result of anoxic sediment conditions. Lower magnitude long-term release conditions were maintained for most of the year, most likely as a result of organic P cycling and maintenance of high concentration gradients between the pore and bottom water P pools. Estimates of summer P uptake/release rates, across an intact sediment-water interface, suggested that maximum gross internal release was ~12 mg SRP m⁻² lake surface area d⁻¹ with EPC0 values ranging between 180 and 270 μg P L⁻¹. This study highlights the biological mediation of internal loading in shallow eutrophic lakes, and in particular, the role of sediment algae in decreasing, and sediment bacteria in enhancing, sediment P release.     

A study of absorption characteristics of chromophoric dissolved organic matter and particles in Lake Taihu,China

Absorptions by non-phytoplankton particles and phytoplankton, and chromophoric dissolved organic matter (CDOM) were measured at 50 sites in large, shallow, Lake Taihu in winter and summer 2006 to study their seasonal and spatial variations, and their relative contributions to total absorption. The CDOM absorption was significantly higher in winter than in summer, due to degradation and release of fixed carbon in phytoplankton and submerged aquatic vegetation (SAV). The hyperbolic model was used to model the spectral absorption of CDOM, and the mean spectral slope of 6.38 nm⁻¹ was obtained. At most sites, the spectral absorption of non-phytoplankton particles was similar to that of the total particles, demonstrating that the absorption of the total particles is dominated by the absorption of non-phytoplankton particles. In summer, phytoplankton absorption increased markedly, due to frequent algal blooms especially in Meiliang Bay. In winter, the significant increase in non-phytoplankton particle absorption resulted from the increase of inorganic particulate matter caused by sediment resuspension. Strong linear relationships were found between a _d(440) and total suspended matter (TSM), organic suspended matter (OSM), and inorganic suspended matter (ISM). Strong linear relationships were also found between a _ph(440), a _ph(675) and chlorophyll a (Chl-a) concentration. The total relative contributions of non-phytoplankton particles over the range of photosynthetically active radiation (PAR) (400–700 nm) were 48.4 and 79.9% in summer and winter respectively. Non-phytoplankton particle absorption dominated the total absorption, especially in winter, in Lake Taihu, due to frequent sediment resuspension in the large shallow lake as a result of strong windy conditions. The results indicate that strong absorption by CDOM and non-phytoplankton particles at the blue wavelength has an impact on the spectral availability, and acts as a selection factor for the composition of the phytoplankton community, with cyanobacteria being the dominate species in Lake Taihu. Handling editor: L. Naselli-Flores